1. Field of the Invention
The present invention pertains to a film image reading device that optically reads an image on film, and more particularly, to a film image reading device equipped with a focus detection function to read the image in the optimal focus condition.
2. Description of the Related Art
Conventionally, the following are known as methods of focus detection using image signals from a video camera. U.S. Pat. No. 5,070,408 proposes a method in which signals that are filtered through a low-pass filter (LPF) having the characteristics of the image sensing lens while the lens is not focused are subtracted from the original signals and the remaining signals are integrated so that the contrast is detected. U.S. Pat. No. 4,980,773 proposes a method in which focus detection is performed by sequentially switching multiple band pass filters (BPFs). A device in which contrast detection is performed based on the photo object image signals using a high-pass filter (HPF) is also known.
Among film image reproduction devices that scan and read the image on the film and reproduce the same on a monitor, etc., there are those capable of focus adjustment in order to maintain a good focus condition. In other words, a device of this type can maintain a good focus condition regardless of what method is used to house the film or whether the film is warped. This device evaluates the focus condition by detecting the contrast of the film image, and while doing so it uses a band pass filter (BPF) effective at the frequency range in which the contrast of the image varies most due to defocusing. In general, an image signal exists in a range up to 30 lines/mm. The contrast of the image decreases due to defocusing, with image signals in the frequency range of 10 to 30 lines/mm. Therefore, a BPF is designed such that only image signals included in this range are allowed to pass.
However, in the methods disclosed in U.S. Pat. Nos. 5,070,408 and 4,980,773 and the film image reproduction device above, it is necessary for the device to have a high image signal filtration performance, and therefore a high order LPF or BPF of a design with complex coefficients must be used. Therefore, the construction of the hardware becomes complex, and at the same time, the time required for the calculation of the focus condition increases.
Further, since processing is performed using image signals, the fact that the frequency characteristics vary depending on the type of photo object must be considered as well.
On the other hand, a device in which the calculated value for the focus condition is displayed on a monitor, etc., based on the result of the film image contrast detection is known. This device has a display scale that does not allow a display exceeding the scale even with a relatively large calculated value because the level of the calculated value for the focus condition varies depending on the film""s ISO sensitivity and film density. In other words, in the case of a film having a film sensitivity level frequently used in general, the display scale is too large and the display of the calculated value for the focus condition becomes relatively small. On the other hand, in the case of a film having a high ISO sensitivity, the displayed value may be so large that it exceeds the display scale.
A purpose of the present invention is to resolve the problems described above.
Another object of the present invention is to provide a film image reading device equipped with an improved focus detection function.
Yet another object of the present invention is to provide a film image reading device that can easily perform focus detection without using complex hardware.
Yet another object of the present invention is to provide a film image reading device in which the calculation time required for focus detection is reduced. Yet another object of the present invention is to provide a film image reading device that can reliably detect the focus condition regardless of the type of the photo object whose image is on the film.
Yet another object of the present invention is to provide a film image reading device equipped with a monitor that can optimally display the calculated value for the focus condition.
Yet another object of the present invention is to provide a film image reading device equipped with a monitor that can optimally display the calculated value for the focus condition regardless of the type of the film used.
These and other objects are attained by a film image reading device having a reading means that reads the image on the film, an image extracting means that extracts signals caused by the graininess of the film from the image signals read, and a calculating means that calculates the image contrast value based on the signals extracted.
These and other objects are also attained by a film image reading device having an optical system that projects the image on the film, a reading means that reads the image projected by the optical system, a signal extracting means that extracts signals caused by the graininess of the film from the image signals read, a calculating means that calculates the image contrast value based on the signals extracted, a moving means that moves the image along the optical axis of the optical system in a relative fashion, and a control means that moves the image to a position where the optimal contrast value may be obtained in accordance with the contrast value calculated.
These and other objects are also attained by a film image reading device having a reading means that reads the image on the film, a calculating means that calculates the contrast value based on the image signals read, an information extracting means that extracts attribute information regarding the film or the image on the film, a normalization means that normalizes the contrast value in accordance with the attribute information extracted, and a display means that displays the normalized contrast value.